1. Field
Exemplary embodiments of the present invention relate to a semiconductor design technology and, more particularly, to a semiconductor memory device which supports high speed operations.
2. Description of the Related Art
In general, semiconductor memory devices perform read data operations on a basic cycle. That is to say, reading data in a semiconductor memory device cell array includes stepwise operations such as active (ACT), read (READ) and precharge (PCG) operations, as shown in FIG. 1. “CLK”, “Command”, “RD”, “Address”, “Bank A ADD(X,Y)” and “Internal operation” shown in FIG. 1 denote “a clock signal”, “a command signal”, “a read command signal”, “an address signal”, “row and column addresses of bank A” and “an internal operation sequence”, respectively. A minimum time tRC is required to perform such stepwise active (ACT), read (READ) and precharge (PCG) operations between successive read operations. The time required between successive operations is determined in part by the physical characteristics of the circuit, including the time that it takes for circuits and capacitors to reach equilibrium after being charged and discharged. This is one limitation on the ability of memory cells to perform read and write operations.
Semiconductor memory device operating speed, including the ability to output data quickly, has been and still is an important design factor. Therefore, the semiconductor industry is constantly looking for ways to improve the speed with which memory cells can be read and be written to.
Conventional semiconductor memory devices have internally divided cell arrays including a plurality of banks that output data independently in order to increase operating speeds. The banks may output data at intervals shorter than ‘tRC’ in such a manner that their operation periods overlap. Therefore, data may be successively outputted within a time shorter than ‘tRC’.
However, although a large number of banks are included in a semiconductor memory device, a minimum time tRC is needed between operations for repeatedly accessing and reading data from the same bank.